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No description available.

Graduate

Thesis (MScIng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Thesis (M.S.)--Tennessee Technological University, 2008. / Title from title page screen (viewed on July 16, 2010). Bibliography: leaves 97-99.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 135-138).

In this dissertation, a variety of semiconductor based transmission lines are investigated. Among them are metal-insulator-semiconductor (MIS) coplanar waveguide (CPW) slow-wave structures and laser diodes. Although laser diodes are electro-optic devices, their microwave parameters are of great importance for broadband matching to their driver networks. It will be shown that, besides their optical characteristics, laser diodes can be regarded as bias-dependent lossy and dispersive slow-wave transmission lines for the driving RF/microwave signal. The analysis of this kind of transmission lines is very difficult or even impossible through a single numerical approach. Therefore, in this thesis a combination of two methods is applied, namely, the complex finite difference method (CFDM) and the frequency-domain transmission line matrix (FDTLM) method. The CFDM provides a self-consistent solution to the semiconductor equations, which determines the conductivity distribution in the semiconductor layer as a function of the bias current. The FDTLM method utilizes this information to calculate the microwave characteristics of such a multilayered, lossy transmission line. The development of the CFDM, based on information available from the literature, is described in detail. For the FDTLM method, an investigation is presented analyzing the errors of the various node representations. On the basis of this investigation, a new node, the hybrid node with shunt decomposition, is developed. This node shows better accuracy than other nodes and is particularly well suited for the analysis of lossy, semiconductor-based structures. Furthermore, by using finite differencing and averaging, the theoretical foundation of the FDTLM method is expanded and, for the first time, a direct relationship between the electromagnetic field and the voltages and currents in the hybrid node with shunt decomposition is established. On the basis of the numerical techniques developed in the first part of the thesis, mode propagation and scattering of electromagnetic field in a variety of semiconductor-based structures are investigated. Besides the microwave effects in semiconductor lasers and the slow-wave characteristics in MIS CPW structures, the second part of this thesis concentrates on the scattering of fields at discontinuities between transmission lines. This includes wire bond and flip-chip transitions between transmission lines and laser diodes as well as direct transitions, for example, between slow-wave CPW structures on doped silicon and CPW on the same but an undoped substrate. Whenever possible, these results are compared with those from other methods and measurements. However, since most of the structures and transitions considered in this thesis are investigated for the first time, the data available in the open literature is limited. From the comparison of obtained results with the available data and measurements one can safely conclude that the numerical analysis presented for all structures is a true picture of the physical reality. / Graduate

D.Ing. (Mechanical Engineering) / This research proposed to develop a mathematical model for the prediction of aeolian vibration levels on overhead transmission lines in order to be able to ensure that damping systems are designed optimally in future. In order to enhance the understanding of aeolian and wake-induced vibration further, it also proposed to implement and apply the fluid flow simulation technique of Computational Fluid Dynamics (CFD) to both single conductors and conductor bundles. The Introduction of the CFD tool to the field of transmission line vibration, will ensure that bundles could be optimally designed for future applications. Wind-induced vibrations are known to cause expensive damage to the conductors and related hardware through fatigue or clashing of the bundled conductors. The primary cause of conductor aeolian vibration is the alternate shedding of wind-induced eddies from the top and bottom sides of the conductor, whereas wake-induced oscillations is peculiar to bundled conductors and arises from effects of the shielding of leeward conductors in bundles by windward ones. In order to study the phenomenon of aeolian vibration, research was undertaken utilising a full scale transmission line test station close to Kroonstad in the Orange Free State. Commercially available computer based packages were used for the development and simulation of both the mathematical model and fluid flow. During the flow simulations, an actual Zebra conductor and Zebra bundle configuration were utilised. For the development of the mathematical model, the pratical results, as measured at the Kroonstad transmission line test station during Phase I, were utilised. From the tests performed during Phase I, it was concluded that the damping solutions, currently used by Eskom as tested during Phase I, are all effective in controlling the aeolian vibration. The Stockbridge damper proved to be avery effective damper. Two models for the prediction of aeolian vibration levels were derived. Results showed that the vibration levels could be estimated to the correct order of magnitude and in many cases the precise values. The accuracy of the model was further improved by the inclusion of the Strouhal number as a function of windspeed. It has been decided by the author 10 develop and design a low cost vibration activity indicator for aeolian vibration measurements. The T-R-I-V-A-I has shown that it is a repeatable, reliable device, Ideally suited for line vibration detection. A new device, the W-I-V-I, has also been designed and implemented by the author for the detection and quantification of wake-induced vibration. During the simulation of the flows around a conductor in the steady state, it was established that the flow around as smooth cylinder and a Zebra conductor, is very similar, however, it was established that the rough outer surface of the Zebra conductor acts as a vortex generator. It has been found that a stability relationship exists between the degree of symmetry of the pressure cell, directly in front of the leeward conductor and the wake-induced vibration. Results for the unsteady flow situation showed the initiation and dispersion of the vortices as they are generated alongside the conductor. It is recommended that the developed model's accuracy be further enhanced. It should be established if .there are families of curves and data that belong together and that contribute to the amount of scatter in the parameters measured such as vibration amplitude, Strouhal number, etc. The applicability of CFD to the transmission line field should be enhanced, with the view of increasing bundle performance, both from an electrical and mechanical point of view.

This thesis was prompted by the belief that local residential streets could be better used and serviced if a common underground structure were provided for all utilities. Such a structure could not only get wiring underground, a desirable aim in itself, but also gather all of the utilities together in a narrow portion of the street. This would free the remainder of the street from the restrictions imposed by the utilities, and allow designers to create more interesting and pleasant environments. It was further believed that such structures might be feasible if the designing and servicing of local streets were considered comprehensively. These beliefs have been investigated by formulating and testing the general hypotheses that installing utilities in specially designed underground structures in local residential streets would: a) permit better use and design of such streets than is possible by current servicing practices; b) be feasible (from functional, physical, social, staging, administrative, political, financial, and economic points of view) if comprehensively designed. The scope of this investigation has been limited to future local streets in single-family residential districts of Metropolitan Vancouver for these reasons. Future streets would allow maximum flexibility in design and savings in servicing costs by proposed practices. Local streets generally have simpler and smaller-sized facilities which are most widely spread. Single-family residential districts are and will be the largest land use and hence, have the most increase in streets. Metropolitan Vancouver has been studied because of its proximity and familiarity to the investigator and its variety of servicing practices. Street use is the use made of streets including such ones as playing not currently facilitated. The 'servicement' is that part of the physical environment created by property service facilities in the streets. Property services are those public services providing service to property as distinct from people. Current practice is the ways of designing and installing facilities followed at the present time. The term 'better' in the first hypothesis is interpreted in terms of elements of the public interest. These include public health, safety, convenience, amenity, welfare, and economy. Criteria of feasibility have been established for the evaluation of the proposed practices. These include functional, physical, social staging, administrative, political, functional, and economic feasibility. They are essentially different ways of looking at a complex problem. [ ... ] / Applied Science, Faculty of / Community and Regional Planning (SCARP), School of / Graduate

In this work, the accurate representation of transmission lines for the digital simulation of electromagnetic transients in power systems has been examined. A model has been developed that accounts for the frequency dependence and distributed nature of the line parameters over the entire frequency range. This model can easily be incorporated into a time-domain network solution of the complete power system. The model consists simply of a constant resistence in parallel with a current source evaluated at each time step of the solution. The equivalent resistance results from a finite-step-width discretization of the differential equations of a resistance-capacitance (R-C) network that simulates the line characteristic impedance. The equivalent current source accounts for the time delays and attenuations of the different frequency components of the travelling waves and for the discretization of the time-domain equations. Rational-function approximations are used to synthesize the R-C network and the line propagation ("weighting") function in the frequency domain. These rational approximations allow the corresponding time-domain functions to be obtained directly in a closed-form, thus circumventing the need for numerical inverse Fourier transformations. The numerical technique used to obtain the rational functions yields very accurate, high-order approximations. This technique is based on a direct, step-by-step allocation (and reallocation) of poles and zeros and avoids the instability problems which can be encountered with optimization techniques based on search methods. A series of analytical evaluations and simulation tests were performed in order to assess the validity of the model. The results of these tests show that the model is accurate, fast, and reliable. The model was incorporated into the code of the University of British Columbia's version of Dr. H.W. Dommel's Electromagnetic Transients Program (EMTP). i / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate